Conventionally, a Ziegler-Natta catalyst system, including a main catalyst component of titanium or vanadium compounds and a cocatalyst component of alkylaluminum compounds, has been used to produce an ethylene homopolymer or copolymers of ethylene and α-olefins. However, the Ziegler-Natta catalyst system is disadvantageous in that, even though it is highly active in the polymerization of ethylene, the molecular weight distribution of resultant polymers is wide, and particularly, the compositional distribution in the copolymers of ethylene and α-olefins is non-uniform due to heterogeneous catalyst active sites.
Recently, a so-called metallocene catalyst system, including a metallocene compound of a group IV transition metal in the periodic table of the elements, such as titanium, zirconium, hafnium, or the like, and methylaluminoxane, which is a co-catalyst, has been developed. The metallocene catalyst system is a homogeneous catalyst system having single catalytic active-site, and is characterized in that the metallocene catalyst system can be used to produce polyethylene having a narrow molecular weight distribution and a uniform composition distribution, compared to the conventional Ziegler-Natta catalyst system. For example, it was disclosed in European Patent Publication No. 320762 and Japanese Patent Publication No. Sho63-092621 that a metallocene compound, such as Cp2TiCl2, Cp2ZrCl2, Cp2ZrMeCl, Cp2ZrMe2, ethylene(IndH4)2ZrCl2, or the like, is activated using methylaluminoxane, which is a co-catalyst, so that ethylene is very actively polymerized, thereby producing polyethylene having a molecular weight distribution (Mw/Mn) ranging from 1.5 to 2.0. However, in the metallocene catalyst system disclosed in the patent documents, it is known that it is difficult to produce a polymer having a high molecular weight using the metallocene catalyst system, that the polymerization activity of the metallocene catalyst system is rapidly decreased and the β-hydride elimination of ethylene is accelerated when the metallocene catalyst system is applied to a solution polymerization method, which is carried out at a high temperature of 140° C. or more, and thus the metallocene catalyst system is not suitable for use in the production of a high molecular weight polymer having a weight-average molecular weight of 100,000 or more.
Meanwhile, a constrained geometry non-metallocene catalyst (a so-called single-site catalyst) in which a transition metal is connected to a ring shape ligand system has been suggested as a catalyst which has a high catalytic activity and is capable of producing a polymer having a high molecular weight in polymerization of only ethylene or in copolymerization of ethylene and a-olefins under solution polymerization condition. European Patent Nos. 0416815 and 0420436 disclose a constrained geometry non-metallocene catalyst in which one cyclopentadiene ligand is bonded with amide groups in a ring shape, and European Patent No. 0842939 discloses a constrained geometry non-metallocene catalyst in which phenol-based ligands, which are electron-donating compounds, are bonded with cyclopentadiene ligands in a ring shape. However, such constrained geometry non-metallocene catalysts are very difficult to use commercially because the yield of a process of cyclization along the transition metal with ligands during the synthesis of the constrained geometry non-metallocene catalyst is very low.
Meanwhile, U.S. Pat. No. 6,329,478 and Korean Patent Publication No. 2001-74722 disclose a non-metallocene catalyst, which is not a constrained geometry catalyst. It can be seen in these patent documents that a single-site catalyst, produced using at least one phosphine-imine compound as a ligand, exhibits a high conversion of ethylene in copolymerization of ethylene and α-olefin under a solution polymerization condition at above 140° C. Further, U.S. Pat. No. 5,079,205 discloses a non-metallocene catalyst including a bis-phenoxide ligand, and U.S. Pat. No. 5,043,408 discloses a non-metallocene catalyst including a chelated bis-phenoxide ligand. However, such non-metallocene catalysts are very difficult to use commercially to produce an ethylene homopolymer or an ethylene-α-olefin copolymer at high temperatures because they have very low catalytic activity.
Furthermore, Japanese Patent Publication Nos. 1996-208732 and 2002-212218 disclose an anilido ligand as an olefin polymerization catalyst, but nowhere is the use of the olefin polymerization catalyst within a commercially useful polymerization temperature range mentioned therein. In addition, the olefin polymerization catalyst is different in structure from the transition metal catalyst, disclosed in the present invention, including an anilido ligand having an aryl substituent at the ortho position thereof. Furthermore, In addition, it was reported in the paper ┌Organometallics 2002, 21, 3043, Nomura et al.┘ describes an anilido ligand as a non-metallocene catalyst for use in polymerization, but the substituent at the ortho position is limited only to the most simple alkyl, methyl.